1. Field of the Invention
The present invention relates to a display device such as a liquid crystal display (LCD) or a plasma display panel (PDP), and more particularly, to an image display apparatus such as a monitor, a television, or a mobile display which includes a display device and displays a subpixel-based color image, an image display method therefor, and a computer-readable recording medium for storing a computer program.
2. Description of the Related Art
FIG. 1 is a diagram showing an example of a filter having an RGB stripe arrangement, used in a conventional image display apparatus. The filter includes a plurality of subpixels.
FIG. 2 is a diagram showing an example of a color filter used in a image display apparatus. The color filter includes a plurality of subpixels.
Referring to FIG. 1, each subpixel displays one color component among red (R), green (G) and (B) color components of an image signal. A single display pixel includes three subpixels displaying R, G and B color components, respectively. The subpixels shown in FIG. 1 are individually controlled to display an image, and therefore, a horizontal resolution triples theoretically when a black and white image is displayed. Each subpixel shown in FIG. 2 displays one color component among R, G, B and white (W) color components. Here, a display pixel includes a plurality of subpixels displaying R, G and B color components, R, W and G color components, G, W and R color components, or G, B and R color components.
Such a conventional image display apparatus, which displays an image by subpixel rendering, can decrease occurrence of a jagged pattern. The jagged pattern usually occurs at a boundary of a fine character such as an italic font when the resolution of an input content is higher than a resolution at which an image display apparatus can display an image.
However, a color image displayed on the conventional image display apparatus displaying an image by subpixel rendering may have a color fringe due to a phase shift of subpixels when a brightness value rapidly changes among the subpixels at a boundary of the color image. The color fringe may be different depending on an arrangement of subpixels. For example, in the stripe arrangement shown in FIG. 1, the color fringe may occur on a diagonal. In a delta arrangement, the color fringe may occur on a vertical straight line. In particular, the color fringe is more prominent when chrominance components are periodically arranged in units of two or more groups of subpixels, as shown in FIG. 2, than when chrominance components are periodically arranged in units of one display pixel as in the stripe arrangement shown in FIG. 1.
A conventional apparatus for displaying an image based on a subpixel is disclosed in U.S. Pat. No. 5,341,153, entitled “Method of and Apparatus for Displaying a Multicolor Image.” In the conventional method and apparatus for displaying a high resolution multicolor image on a lower resolution display, a single image pixel is expressed with being divided into subpixels displaying R, G and B color components to increase the resolution of the display. However, such a conventional image display method and apparatus in which a subpixel of interest is expressed by an average of adjacent image pixels have disadvantages of increasing image blurring and causing a color fringe when brightness rapidly changes among chrominance components.
FIG. 3 is a graph illustrating characteristics of human sight according to a spatial frequency of an image. In the graph, the horizontal axis indicates cycles per degree (c/d), and the vertical axis indicates contrast sensitivity.
Unlike the conventional image display method and apparatus in which a subpixel is expressed by an average of adjacent image pixels, another conventional image display method and apparatus in which a chrominance component of a subpixel is expressed in consideration of characteristics of human sight is disclosed in U.S. Patent Publication No. 2002/0093521 A1, entitled “Methods and Systems for Improving Display Resolution in Images Using Subpixel Sampling and Visual Error Filtering.” In the conventional image display method and apparatus disclosed in U.S. Patent Publication No. 2002/0093521 A1, a luminance value of a chrominance component to be expressed by a subpixel is calculated using an optimal filter that is designed in consideration of the characteristics of human sight, i.e., a theoretical visibility range of a user, thereby improving a display resolution. As shown in FIG. 3, the human sight is very sensitive to the luminance Contrast Sensitivity Function (CSF) of an image but is less sensitive to a chrominance component such as red-green CSF or blue-yellow CSF of the image. However, since the optimal filter is designed in consideration of the theoretical visibility range, the above-described image display method and apparatus are not suitable for a mobile environment, i.e., when a fluid visibility range needs to be secured to display an image. Moreover, since the conventional image display method and apparatus use the filter designed to operate in an opponent color space, unnecessary complex color space conversion is required.
In addition, in the conventional image display methods and apparatuses, each subpixel displays only one among three colors, as shown in FIG. 1, but a high-resolution color image cannot be displayed without a color fringe when each subpixel displays one among four colors, as shown in FIG. 2, or one among more than four colors.